Unbalanced PDC drill bit with right hand walk tendencies, and method of drilling right hand bore holes

Abstract

A rotary drill bit for cutting an earth formation is provided. The drill bit includes a bit body rotatable about its longitudinal axis. A cutting face is provided on the bit body, with a concave central region and a raised outer periphery terminating at bit shoulder. The bit shoulder is concentric with and substantially parallel to the longitudinal axis of the rotary drill bit. A plurality of bit stabilizing pads are circumferentially disposed about the bit's shoulder. A plurality of stationary cutter elements are fixedly mounted to the cutting face in a selected pattern to provide a region of high cutter density on one side of the cutting face, and a region of low cutter density on the other side of the cutting face. The drill bit cuts earth formations as the bit body is rotated about its central axis. The stationary cutter elements operate to cut into the lower side wall of the wellbore as the bit body is rotated, causing the rotary drill bit to walk to the right.

What is claimed is: 
     
       1. A rotary drill bit for cutting in earth formations, for use in a deviated wellbore which extends downward from a surface and includes an upper sidewall region and a lower sidewall region, comprising: a bit body rotatable about its longitudinal axis;   a cutting face on said bit body, with a concave central region and a raised outer periphery terminating at a bit shoulder, said bit shoulder being concentric with and substantially parallel to said longitudinal axis;   a plurality of bit stabilizing pads circumferentially disposed about said bit shoulder;   a plurality of stationary cutter elements fixedly mounted to said cutting face in a selected pattern to provide a region of high cutter density on one side of said cutting face and a region of low cutter density on the other side of said cutting face, for cutting said earth formation as said bit body is rotated about said central axis; and   wherein said stationary cutter elements operate to cut into said lower sidewall of said wellbore as said bit body is rotated, causing said rotary drill bit to walk to the right.   
     
     
       2. A rotary drill bit for cutting in earth formations according to claim 1, further comprising: a plurality of fluid discharge nozzles terminating at said cutter face for emitting a pressurized drilling fluid to flush and cool said drill bit.   
     
     
       3. A rotary drill bit for cutting in earth formations according to claim 1, wherein said cutters comprise polycrystalline diamond compact cutters. 
     
     
       4. A rotary drill bit for cutting in earth formations according to claim 1, wherein said region of high cutter density occupies a region on said cutting face between 72 degrees and 175 degrees relative to a center point on said cutting face. 
     
     
       5. A rotary drill bit for cutting in earth formations according to claim 1, wherein said region of high cutter density comprises a generally triangular region of less than 175 degrees relative to a center point on said cutting face, which includes at least the first six cutters positioned on said cutting face radially outward from a center point on said cutting face. 
     
     
       6. A rotary drill bit for cutting in earth formations according to claim 1, wherein said region of high cutter density comprises a generally triangular region of less than 175 degrees relative to a center point on said cutting face, which includes at least the first four cutters positioned on said cutting face radially outward from said center point on said cutting. 
     
     
       7. A rotary drill bit for cutting in earth formations according to claim 1, wherein said cutters comprise polycrystalline diamond compact cutters having a diameter less than 0.71 inches each, wherein said region of high cutter density comprises a region defined by the placement of the first six cutters positioned on said cutting face radially outward from a center point on said cutting face. 
     
     
       8. A rotary drill bit for cutting in earth formations according to claim 1, wherein said cutters comprise polycrystalline diamond compact cutters having a diameter equal to or greater than 0.71 inches each, wherein said region of high cutter density comprises a region defined by the placement of the first four cutters positioned radially outward from a center point on said cutting face. 
     
     
       9. A rotary drill bit for cutting in earth formations according to claim 1, wherein said cutters comprise polycrystalline diamond compact cutters having a diameter less than 0.71 inches, wherein said region of high cutter density comprises a region defined by the placement of at least the first six cutters positioned on said cutting face radially outward from a center point on said cutting face, and wherein said region of low cutter density includes a region with no cutters opposite from said region of high cutter density between said center point and a radial boundary established by the first cutter positioned radially outward from said center point which is placed opposite said region of high cutter density. 
     
     
       10. A rotary drill bit for cutting in earth formations according to claim 1, wherein said cutters comprise polycrystalline diamond compact cutters having a diameter equal to or greater than 0.71 inches, wherein said region of high cutter density comprises a region defined by the placement of at least the first four cutters positioned on said cutting face radially outward from a center point on said cutting face, and wherein said region of low cutter density includes a region with no cutters opposite from said region of high cutter density between said center point and a radial boundary established by the first cutter positioned radially outward from said center point which is placed opposite said region of high cutter density. 
     
     
       11. A rotary drill bit for cutting in earth formations for use in a deviated wellbore which extends downward from a surface and includes an upper sidewall region and a lower sidewall region, comprising: a bit body rotatable about its longitudinal axis;   a cutting face on said bit body, with a concave central region and a raised outer periphery terminating at a bit shoulder, said bit shoulder being concentric with and substantially parallel to said longitudinal axis;   a plurality of bit stabilizing pads circumferentially disposed about said bit shoulder, selected ones of said stabilizing pads have a first radial width relative to said longitudinal axis which is less than a second radial width of selected others of said stabilizing pads;   a plurality of stationary cutter elements fixedly mounted to said cutting face in a selected pattern to provide a region of high cutter density on one side of said cutting face and a region of low cutter density on the other side of said cutting face, for cutting said earth formation as said bit body is rotated about said central axis; and   wherein said stationary cutter elements operate to cut into said lower sidewall of said wellbore as said bit body is rotated, causing said rotary drill bit to walk to the right.   
     
     
       12. A rotary drill bit for cutting in earth formations for use in a deviated wellbore which extends downward from a surface and includes an upper sidewall region and a lower sidewall region, comprising: a bit body rotatable about its longitudinal axis;   a cutting face on said bit body, with a concave central region and a raised outer periphery terminating at a bit shoulder, said bit shoulder being concentric with and substantially parallel to said longitudinal axis;   a plurality of bit stabilizing pads circumferentially disposed about said bit shoulder, selected ones of said stabilizing pads have a first radial width relative to said longitudinal axis which is less than a second radial width of selected others of said stabilizing pads, and wherein said stabilizing pads having said first radial width are disposed along said bit shoulder adjacent said region of high cutter density, placing said region of high cutter density in close proximity to said lower sidewall region during at least a portion of the drill bit rotation and allowing said cutter elements to cut into said lower sidewall of said wellbore.   a plurality of stationary cutter elements fixedly mounted to said cutting face in a selected pattern to provide a region of high cutter density on one side of said cutting face and a region of low cutter density on the other side of said cutting face, for cutting said earth formation as said bit body is rotated about said central axis; and   wherein said stationary cutter elements operate to cut into said lower sidewall of said wellbore as said bit body is rotated, causing said rotary drill bit to walk to the right.   
     
     
       13. A rotary drill bit for cutting in earth formations for use in a deviated wellbore which extends downward from a surface and includes an upper sidewall region and a lower sidewall region, comprising: a bit body rotatable about its longitudinal axis;   a cutting face on said bit body, with a concave central region and a raised outer periphery terminating at a bit shoulder, said bit shoulder being concentric with and substantially parallel to said longitudinal axis;   a plurality of bit stabilizing pads circumferentially disposed about said bit shoulder;   a plurality of stationary cutter elements fixedly mounted to said cutting face in a selected pattern to provide a region of high cutter density on one side of said cutting face and a region of low cutter density on the other side of said cutting face, for cutting said earth formation as said bit body is rotated about said central axis;   a portion of said bit body underlying the side of said cutting face which carries said region of high cutter density has a greater weight than a portion of the bit underlying the opposite side of said cutting face which carries said region of low cutter density;   wherein said stationary cutter elements operate to cut into said lower sidewall of said wellbore as said bit body is rotated, causing said rotary drill bit to walk to the right.   
     
     
       14. A rotary drill bit for cutting in earth formations, for use in a deviated wellbore which extends downward from a surface and includes an upper sidewall region and a lower sidewall region, comprising: a bit body rotatable about its longitudinal axis;   a cutting face on said bit body, with a concave central region and a raised outer periphery terminating at a bit shoulder, said bit shoulder being concentric with and substantially parallel to said longitudinal axis;   a plurality of bit stabilizing pads circumferentially disposed about said bit shoulder, selected ones of said stabilizing pads having a first radial width relative to said longitudinal axis less than a second radial width of selected others of said stabilizing pads;   a plurality of stationary cutter elements fixedly mounted to said cutting face in a selected pattern to provide a region of high cutter density on one side of said cutting face and a region of low cutter density on the other side of said cutting face, for cutting said earth formation as said bit body is rotated about said central axis; and   wherein said stationary cutter elements operate to cut into said lower sidewall of said wellbore as said bit body is rotated, causing said rotary drill bit to walk to the right.   
     
     
       15. A rotary drill bit for cutting in earth formations according to claim 14, further comprising: a plurality of fluid discharge nozzles terminating at said cutter face for emitting a pressurized drilling fluid to flush and cool said drill bit.   
     
     
       16. A rotary drill bit for cutting in earth formations according to claim 14, wherein said cutters comprise polycrystalline diamond compact cutters. 
     
     
       17. A rotary drill bit for cutting in earth formations according to claim 14, wherein said stabilizing pads having said first radial width are disposed on said bit shoulder on the side of said cutting face which includes said region of high cutter density, placing said region of high cutter density in close proximity to said earth formation at said lower sidewall during at least a portion of the drill bit rotation. 
     
     
       18. A rotary drill bit for cutting in earth formations according to claim 14, wherein a portion of said bit body underlying the side of said cutting face which carries said region of high cutter density is heavier than a portion of the bit body underlying the opposite side of said cutting face which carries said region of low cutter density. 
     
     
       19. A rotary drill bit for cutting in earth formations according to claim 14, wherein said region of high cutter density occupies a region on said cutting face between 72 degrees and 175 degrees relative to a center point on said cutting face. 
     
     
       20. A rotary drill bit for cutting in earth formations according to claim 14, wherein said region of high cutter density comprises a generally triangular region of less than 175 degrees relative to a center point on said cutting face, which includes at least the first six cutters positioned on said cutting face radially outward from said center point on said cutting face. 
     
     
       21. A rotary drill bit for cutting in earth formations according to claim 14, wherein said region of high cutter density comprises a generally triangular region of less than 175 degrees relative to a center point on said cutting face, which includes at least the first four cutters positioned on said cutting face radially outward from said center point on said cutting. 
     
     
       22. A rotary drill bit for cutting in earth formations according to claim 14, wherein said cutters comprise polycrystalline diamond compact cutters having a diameter less than 0.71 inches each, wherein said region of high cutter density comprises a region defined by the placement of the first six cutters positioned on said cutting face radially outward from a center point on said cutting face. 
     
     
       23. A rotary drill bit for cutting in earth formations according to claim 14, wherein said cutters comprise polycrystalline diamond compact cutters having a diameter greater than 0.71 inches each, wherein said region of high cutter density comprises a region defined by the placement of the first four cutters positioned radially outward from a center point on said cutting face. 
     
     
       24. A rotary bit drill for cutting in earth formations, for use in a deviated wellbore which extends downward from a surface and includes an upper sidewall region and a lower sidewall region, comprising: a bit body rotatable about its longitudinal axis;   a cutting face on said bit body, with a concave central region and a raised outer periphery terminating at a bit shoulder, said bit shoulder being concentric with and substantially parallel to said longitudinal axis;   a plurality of bit stabilizing pads circumferentially disposed about said bit shoulder wherein selected ones of said stabilizing pads have a first radial width relative to said longitudinal axis less than a second radial width of selected others of said stabilizing pads; and   a plurality of stationary cutter elements fixedly mounted to said cutting face in a selected pattern, wherein said stationary cutter elements operate to cut into said lower sidewall of said wellbore as said bit body is rotated, causing said rotary drill bit to walk to the right.   
     
     
       25. A rotary drill bit for cutting in earth formations according to claim 24, further comprising: a plurality of fluid discharge nozzles terminating at said cutter face for emitting a pressurized drilling fluid to flush and cool said drill bit.   
     
     
       26. A rotary drill bit for cutting in earth formations according to claim 24, wherein said plurality of stationary cutter elements include a region of high cutter density on one side of said cutting face and a region of low cutter density on the other side of the cutting face, and wherein said stabilizing pads having said first radial width are disposed along said bit shoulder adjacent said region of high cutter density, placing said region of high cutter density in close proximity to said earth formation at said lower sidewall region of said wellbore during at least a portion of the drill bit rotation. 
     
     
       27. A rotary drill bit for cutting in earth formations according to claim 24, wherein said cutters comprise polycrystalline diamond compact cutters. 
     
     
       28. A rotary drill bit for cutting in earth formations according to claim 24, wherein a portion of said bit body underlying the side of said cutting face which carries said region of high cutter density has a greater weight than a portion of the bit body underlying the opposite side of said cutting face which carries said region of low cutter density. 
     
     
       29. In a nonvertical wellbore, which extends downward from a surface into earth formations, which is deviated radially outward from a vertical axis, and which includes a wellbore bottom having a formation cone and an upper sidewall region above a lower sidewall region, a method of directional drilling, comprising: providing a drill string coupled to a drill bit, said drill bit including a cutting face with a region with a high concentration of cutter elements relative to other regions of said cutting face;   providing a plurality of stabilizing pads radially disposed about said drill bit including at least one undersized stabilizing pad, said at least one undersized stabilizing pad aligned with said region with said high concentration of cutter elements;   rotating said drill string and connected drill bit in a clockwise direction to cut said earth formation;   wherein during a formation cutting half cycle of said rotation said at least one undersized stabilizing pad is oriented downward into contact with said lower sidewall and said drill bit drops off said formation cone by force of gravity to cut said earth formation with said region of high concentration of cutter elements;   wherein during a cone cutting half cycle of said rotation said at least one undersized stabilizing pad is oriented upward into contact with said upper sidewall and said region of high concentration of cutter elements cuts said formation cone;   wherein the repeated and combined cutting of said lower sidewall and said formation cone causes said drill bit to turn to the right.   
     
     
       30. A rotary bit drill for cutting in earth formations, for use in a deviated wellbore which extends downward from a surface and includes an upper sidewall region and a lower sidewall region, comprising: a bit body rotatable about its longitudinal axis;   a cutting face on said bit body, with a concave central region and a raised outer periphery terminating at a bit shoulder, said bit shoulder being concentric with and substantially parallel to said longitudinal axis;   a plurality of bit stabilizing pads circumferentially disposed about said bit shoulder;   a plurality of stationary cutter elements fixedly mounted to said cutting face in a selected pattern to provide a region of high cutter density on one side of said cutting face and a region of low cutter density on the other side of said cutting face, for cutting said earth formation as said bit body is rotated about said central axis; and   said stationary cutter elements have a flat cutting area facing substantially in the direction of rotation of said drill bit whereby said cutter elements operate to cut into said lower sidewall of said wellbore as said bit body is rotated causing said rotary drill bit to walk to the right.   
     
     
       31. A rotary drill bit for cutting in earth formations according to claim 30, wherein said region of high cutter density occupies a region on said cutting face between 72 degrees and 175 degrees relative to a center point on said cutting face. 
     
     
       32. A rotary drill bit for cutting in earth formations according to claim 30, wherein said region of high cutter density comprises a generally triangular region of less than 175 degrees relative to a center point on said cutting face, which includes at least the first six cutters positioned on said cutting face radially outward from a center point on said cutting face. 
     
     
       33. A rotary drill bit for cutting in earth formations according to claim 30, wherein said region of high cutter density comprises a generally triangular region of less than 175 degrees relative to a center point on said cutting face, which includes at least the first four cutters positioned on said cutting face radially outward from said center point on said cutting. 
     
     
       34. A rotary drill bit for cutting in earth formations according to claim 30, wherein said cutters comprise polycrystalline diamond compact cutters having a diameter less than 0.71 inches each, wherein said region of high cutter density comprises a region defined by the placement of the first six cutters positioned on said cutting face radially outward from a center point on said cutting face. 
     
     
       35. A rotary drill bit for cutting in earth formations according to claim 30, wherein said cutters comprise polycrystalline diamond compact cutters having a diameter equal to or greater than 0.71 inches each, wherein said region of high cutter density comprises a region defined by the placement of the first four cutters positioned radially outward from a center point on said cutting face. 
     
     
       36. A rotary drill bit for cutting in earth formations according to claim 30, wherein said cutters comprise polycrystalline diamond compact cutters having a diameter less than 0.71 inches, wherein said region of high cutter density comprises a region defined by the placement of at least the first six cutters positioned on said cutting face radially outward from a center point on said cutting face, and wherein said region of lower cutter density includes a region with no cutters opposite from said region of high cutter density between said center point and a radial boundary established by the first cutter positioned radially outward from said center point which is placed opposite said region of high cutter density. 
     
     
       37. A rotary drill bit for cutting in earth formations according to claim 30, wherein said cutters comprise polycrystalline diamond compact cutters having a diameter equal to or greater than 0.71 inches, wherein said region of high cutter density comprises a region defined by the placement of at least the first four cutters positioned on said cutting face radially outward from a center point on said cutting face, and wherein said region of low cutter density includes a region with no cutters opposite form said region of high cutter density between said center point and a radial boundary established by the first cutter positioned radially outward from said center point which is placed opposite said region of high cutter density.